1. Field of the Invention
The subject invention relates to methods and apparatus for winding and unwinding webs of material or tapes and to tape or web transports and, for instance, has utility in magnetic tape transports and recording equipment, photographic film handling apparatus, cameras and projectors, and other tape or web transporting or handling equipment, particularly systems having different advance modes for tape, film or other web-like material, herein sometimes generically referred to simply as "tape."
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments subsequent in time or priority.
In tape advancing methods and apparatus, tape is frequently advanced in engagement with one or more devices for acting on the tape. By way of example, in magnetic recording and playback systems, tape is typically advanced with an information recording surface in engagement with an information transducing head, such as a recording and playback head or head stack. In such instances, it is frequently desirable, for the purpose of time preservation or otherwise, that the particular recording and playback system has fast forward and rapid rewind facility, as far as the advancement of the tape between, preparatory to and after information recording and playback operations is concerned.
In general, it would be desirable in terms of head and tape life, attainable tape speed and other factors, that the tape be out of engagement with any transducing head during fast tape advance and rapid rewind operations. Many existing systems employ movable transducing heads to this end; moving the head or heads out of engagement with the tape between recording and playback operations. In practice, this frequently has the disadvantage of requiring special head carrying and moving devices or systems which, in high quality applications and equipment, tend to be rather expensive and demanding in terms of requisite precision and which are often not feasible.
Another proposal employs fluid pressure for applying a force on the tape at a position between a transducer assembly and capstan which forces the tape away from the capstan towards the transducer assembly, as may be seen from U.S. Pat. No. 3,688,956 by Magne J. Kjos, issued Sept. 5, 1972. U.S. Pat. No. 3,645,471, by the latter inventor, issued Feb. 29, 1972, discloses apparatus for guiding tape between two planes.
In terms of general applicability, an apparent drawback of that proposal is that it has to rely on the consistent maintenance of a positive fluid pressure gradient for a reliable application of the tape to the information transducing head and that it, moreover, inevitably calls for a partial separation of the tape from the driving capstan during the recording and playback process. On the other hand, it appears that the tape would remain in contact with a large and bulky capstan during attempted tape forward and rewind operations, thereby impeding attainable rapid tape speed.
Reference may in this respect also be had to my prior U.S. Pat. No. 3,986,651, issued Oct. 19, 1976 and showing concave vacuum tape guides along which tape was slid during recording and playback operations. That prior system inherently lacked a real tape fast forward and rapid rewind facility; inherently restricting tape advance and rewind to only about three times tape velocity during recording and playback. Also in that prior proposal, the tape remained applied to air bearing tape guides during the entire operation of the tape transport, and retractable heads would be necessary if disengagement of the tape from recording and playback heads were desired.
U.S. Pat. No. 4,065,044, by Alan Painter et al, issued Dec. 27, 1977, proposed a reversal of a vacuum capstan to an air supply system for achieving a separation of a tape from its capstan. This at least required the provision of a rather complicated capstan structure.
Similar considerations apply to proposals which circumvent the tape drive capstan during a tape threading operation, as may be seen from U.S. Pat. Nos. 3,645,472, by Audeh, 3,823,895, 3,826,446 and 3,916,411, by Jones, 3,863,863, by Ende and 3,892,007 by Pembroke.
Various other proposals engage the tape for the purpose of moving it into and out of engagement with recording and playback heads. Such proposals generally have the disadvantage of requiring recurring contact of the tape recording surface or layer with mechanical tape moving means, or of requiring movement of the tape in engagement with finger or rod-like tape moving elements, frequently about a relatively small radius, as may, for instance, be seen from U.S. Pat. No. 3,612,539, by Peter Bragas, issued Oct. 12, 1971.
U.S. Pat. No. 3,779,481, by H. Wilson, issued Dec. 18, 1973, discloses a vacuum buffer in which tape is lifted off transducing heads by atmospheric pressure. U.S. Pat. No. 3,254,854, by W. W. Deighton et al, issued June 7, 1966, discloses tape handling apparatus in which tape is kept in engagement with a guide block, even in an information transducing mode.